Air Pollution Makes Flowering Plants Harder to Locate for Pollinators, Study Finds

A white-lined sphinx moth on an evening primrose flower in Salt Lake County, Utah. These pollinators, also known as hummingbird moths, could not find the flowers in a study involving air pollution. Tony Frates / Flickr

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A new study has revealed that the chemicals in air pollution may be disrupting plant reproduction, as the pollutants mask the scent of flowering plants and make them more difficult for pollinators to find.

The study, published in the journal Science, showed how nitrate radicals (NO₃), which can form from combustion in gas-fueled vehicles and coal and gas power plants, and ozone pollutants can degrade the natural chemical scents of flowers.

“When you smell a rose, you’re smelling a diverse bouquet composed of different types of chemicals,” Jeff Riffell, a co-lead author of the study and biology professor at the University of Washington, explained in a statement. “The same is true for almost any flower. Each has its own scent made up of a specific chemical recipe.”

Researchers analyzed the scent samples from evening primrose flowers, then observed how each natural chemical in the flowers’ scents reacted with the pollutants in wind tunnels and field experiments. The researchers found that the nitrate radicals masked certain chemicals, including monoterpenes, which are particularly attractive to moths.

While both nitrate radicals and ozone pollutants had an effect on the flowers’ scents, nitrate radicals had a bigger impact on the monoterpenes that moths rely on to find and pollinate flowers.

The researchers found that in the wind tunnel experiments, tobacco hawkmoths were 50% less accurate in locating the flowers, and white-lined sphinx moths weren’t able to find the flowers at all. In the field experiments, moths had up to a 70% decline in accuracy of finding the flower sources when nitrate radicals were introduced.

“The NO3 is really reducing a flower’s ‘reach’ — how far its scent can travel and attract a pollinator before it gets broken down and is undetectable,” Riffell explained.

According to the researchers, primroses could experience more difficulty in producing seeds, by about 28%, because of the inability of moths to find the flowers, Popular Science reported. This estimate applied only to the affect of the disruption to moths pollinating primroses, so negative implications could be more widespread. 

“Pollinators play a huge role in community ecology; they’re critical for the fitness of plants. If you affect that, then you’re going to have ecosystem-wide impacts,” Riffell told Popular Science. “Pollinators are also critical for our food system and food security.” 

In January, scientists published a separate study on the potential impacts of air pollution on insect pollination. That study similarly noted how air pollutants can hinder floral scents as well as visual cues, such as plant petal size and potentially color. 

The growing research on how air pollutants impact pollinators and plants highlights the urgency of reducing human-caused pollution. According to the Center for Biological Diversity, 40% of global insect pollinators are endangered. If pollutants are altering the insects’ ability to find plants, it further threatens the pollinators and the plants’ reproduction.

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